CHI straight guard or CHI silk infusion?

I'm going to the store to buy it soon and I'm not sure which one. I really want both. I heard thatif you put the straight guard in and the blow dry it it makes is like straight. I have wavish hair so i was hoping this would help and i heard so many great things about the silk infusion that i dont know which one. i only want to buy one so yeahhhhhhh